This invention generally relates to a system and apparatus for detecting and signaling the presence of an undesired misalignment of one or more of several aligned elements, and more particularly, to a system for monitoring the alignment of a series of adjacent slats or flaps on an aircraft wing.
High lift devices for commercial aircraft wings are sometimes referred to as auxiliary airfoils. Such devices or airfoils are extended from the leading or trailing edges of the wing to increase aerodynamic lift during takeoff and landing of the aircraft. When extended from the wing, the high lift devices increase the effective size, curvature, camber and area of the wing, thereby increasing the lift of the wing for slow speed flight. High lift devices extending from the leading edge of the wing on most airplanes are usually known as slats and those extending from the trailing edge of the wing are known as flaps.
Normally, each high lift device is deployed by two separate but coordinated drive mechanisms, one on the inboard side and the other on the outboard side of the high lift device. Should one of these mechanisms be unable to perform its function, a skewing of the high lift device may occur and jamming or loss of the high lift device may result.
The majority of modern airplane high lift drive systems use actuation methods where all flap drive system elements are driven in synchronization. An element losing synchronization with the rest of the system may cause a skewed flap, that is, a high lift flight control surface that is in an asymmetrical position with respect to the wing""s fixed structure. Undetected skewed flaps are a cause for concern due to the possibility of unpredictable airplane handling characteristics. A skewed flap generates more or less lift than a normally positioned flap, causing asymmetric lift between the two wing surfaces. If the asymmetry is too great, the handling characteristics of the airplane may suffer. If the skew exceeds what the structural capability of the flap can withstand, the flap may sustain structural damage or may undergo structural failure and depart from the airplane structure. A departed flap may negatively impact the aircraft""s handling and controllability, causing undesirable aerodynamic conditions. Also, a departing flap may cause collateral damage to other parts of the airplane if it strikes another part of the airplane.
Recent airplane certification requirements have reacted to this concern by mandating the incorporation of flap skew detection systems in new airplane designs. A problem in designing such a system is that it must be sensitive enough to detect failures before they become a problem while not generating nuisance warnings or shut-downs because of the relatively small skewing movements caused by normal structural deflections, vibrations, dynamics of the aircraft and temperature changes that would not adversely affect airplane handling characteristics. One example of a known flap skew detection method is illustrated in U.S. Pat. No. 5,680,124. In this method, a detector detects the movement of the flap as a target on the flap moves past the sensor. However, the targets must be of a size large enough to be detected by the sensor at a specified distance. Depending on the target""s distance from the sensor and the relative size of the flap stroke, the preciseness of the skew detection may be less than desirable for certain applications. This may lead to an excessive number of false skew alarms or too few alarms, depending on the alarm parameters set for the system.